1. Field of the Invention
This invention relates to downsampling of binary images, and more particularly it relates to topology-preserving down-sampling of binary images.
2. Description of Related Art
Digital image downsampling is widely used in today's computer graphic and image processing applications. Various approaches have been introduced to reduce image quality loss in a down-sampling process.
For example, U.S. Pat. No. 6,563,964 disclosed an image downsampling method using a redundant pixel removal approach for computer-graphics imagery applications, where a digital image is downsampled non-uniformly in a manner that attempts to minimize aliasing of high-spatial-frequency image information by concentrating deletion paths in lower-spatial-frequency image regions, by using a spatial frequency estimator that compares groups of pixels in order to produce a classification of the image, a path generator and path scorer that traces and scores potential deletion paths through the image where the path with the greatest score (i.e., one that provides minimal distortion and aliasing) is selected for pixel removal, and a re-cursor that repeats this process until a desired number of image rows and/or columns have been removed.
Another example is found by E. Decencière, and M. Bilodeau, “Downsampling of Binary Images Using Adaptive Crossing Numbers”, in C. Ronse, L. Najman and E. Decencière editors, Mathematical Morphology: 40 Years On (Proceedings of ISMM'2005), pp. 279-288, (Paris, France, April 2005. Springer), which described a technique using adaptive crossing numbers for downsampling of binary images.
The prior arts described above may have some effects to preserve the topology of the binary images, but they are complex and slow in practice. However, it is still desirable to have a simple and fast method for downsampling of binary images that preserves the topology of the binary images.